Multilayer automotive paint system

ABSTRACT

A transparent topcoat coating composition is described comprising a thermoplastic or thermosetting resin material containing low pigment to binder ratio of iron oxide encapsulated mica particles. When used in a multicoat coating process as a transparent topcoat, an article is produced which not only produces improved &#34;metallic&#34; color effects, but is stable to the elements as well.

This application is a continuation of Ser. No. 631,041 filed July 16,1984, now abandoned, which is a division of copending application Ser.No. 526,724, filed on Aug. 26, 1983, now U.S. Pat. No. 4,499,143.

DESCRIPTION

1. Technical Field

The field of art to which this invention pertains is coatingcompositions, coating methods, and the resultant coated articles.

2. Background Art

Multicoat coating systems are now well known in the coating industry.U.S. Pat. No. 3,639,147 describes such a system for use as an automotivepaint. When multicoat coating systems have previously been applied, ithas been difficult to obtain coatings having uniformly high gloss whileat the same time maintaining good color, and pearlescent features.

In the automotive industry two significant systems are utilized in thepainting of automobiles. One topcoat system which utilizes thermoplasticresins is known as the acrylic lacquer system. In this system the basepolymers are the homopolymers of methyl methacrylate and copolymers ofmethyl methacrylate and acrylic acid, methacrylic acid, alkyl esters ofacrylic acid or methacrylic acid, vinyl acetate, acrylonitrile, styreneand the like. The acrylic lacquer topcoats have been acknowledged tohave outstanding aesthetic properties. Another outstanding topcoatsystem used in the automotive industry is the thermosetting acrylicresins as described in U.S. Pat. No. 3,375,227, issued March 26, 1968.

These topcoat systems have outstanding chemical resistance, outstandingresistance to cracking and crazing among other outstanding properties,but to the expert paint formulator, the thermosetting acrylic resinshave not, in the past, quite provided the aesthetic properties obtainedin the acrylic lacquer systems. In these systems a pigmented base coatcomposition is applied to the metal substrate to hide metallic blemishesand provide the aesthetically pleasing colors desired followed by theapplication of an unpigmented layer of polymer which imparts a "deep"color appearance to the base coat and durability to this pigmented basecoat. This system, however, is not without its problems. Aestheticquality of the coating is totally dependent on the application of thebase coat. The clear topcoat magnifies any weakness in this base coatincluding the highlighting of any color deficiencies of the base coat.The clear coat also acts as a magnifying mirror for ultravioletradiation which can accelerate rather than retard any degradation of thebase coat due to exposure to ultraviolet radiation. In addition, many ofthese coating systems in use today utilize metal particles in the basecoat to provide an aesthetically pleasing metallic appearance. However,problems have occurred with the use of metallic pigments resulting incolor loss in the base coat.

In order to overcome the deficiencies of the metallic pigments,pearlescent pigments have been considered for use in the base coat,either with or in place of conventional pigments. However, use of thesepigments have included such problems as moisture sensitivity, problemswith large particle sizes, application control problems, problems withcolor travel (face to flop), sensitivity to sunlight, subtractive coloreffects, and quality control problems. Both with metallic pigments andwith the many pearlescent pigments available problems such as ghosting,mottling, silking, alligatoring, telegraphing, etc. have also beenobserved. Use of a three coat system can correct some of these problems.However, this is not an acceptable solution in the industry. Additionalcoating steps can only aggravate already insurmountable applicationcontrol problems.

Accordingly, what is needed in this art are improved coatingcompositions and coating systems which are aesthetically pleasing aswell as durable and easy to control.

DISCLOSURE OF INVENTION

A coating composition is disclosed comprising a thermoplastic orthermosetting polymer composition containing iron oxide encapsulatedmica particles in a pigment to binder ratio of about 0.0001 to 0.32(weight ratio). The mica particles are about 5 to about 60 micronsnominal longitudinal dimension and have a thickness of about 0.25 toabout 1 micron. The encapsulating layer constitutes about 10% to about85% by weight of the particle weight. The iron oxide layer can containother constituents such as minor amounts of chromium hydroxide andtitanium dioxide.

Another aspect of the invention includes a substrate material havingcoated thereon a multilayer coating system comprising at least one basecoat and at least one topcoat. The base coat is a pigmented resin. Thetopcoat is a transparent thermoplastic or thermosetting materialcontaining iron oxide encapsulated mica particles as described above.

Another aspect of the invention includes a method of coating a substrateby depositing a layer of the pigmented base coat and applying a layer oftransparent thermoplastic or thermosetting iron oxide encapsulated micacontaining polymer composition described above thereon.

By utilizing the compositions and processes of this invention, not onlyare truer, more brilliant "metallic" colors produced without the needfor metal particles, but colors durable to the elements are produced aswell.

The foregoing, and other features and advantages of the presentinvention, will become more apparent from the following description andaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The Figure shows in cross section a photomicrograph of an iron oxideencapsulated mica containing transparent topcoat according to thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

While any substrate material can be coated with the coating compositionsaccording to the present invention, including such things as glass,ceramics, asbestos, wood, and even plastic material depending on thespecific drying and/or curing requirements of the particularcomposition, the coating system of the present invention is particularlyadapted for metal substrates, and specifically as an automotive paintfinish system. The substrate may also be bare substrate material or canbe conventionally primed, for example to impart corrosion resistance.Exemplary metal substrates include such things as steel, aluminum,copper, magnesium, alloys thereof, etc. The components of thecomposition can be varied to suit the temperature tolerance of thesubstrate material. For example, the components can be so constitutedfor air drying (i.e., ambient), low temperature cure (e.g., 150° F.-180°F.), or high temperature cure (e.g., over 180° F.).

The base coat material, i.e., the pigmented polymer layer closest to thesubstrate, comprises any suitable film forming material conventionallyused in this art including acrylics, alkyds, polyurethanes, polyestersand aminoplast resins. Although the base coat can be deposited out of anaqueous carrier, it is preferred to use conventional volatile organicsolvents such as aliphatic, cycloaliphatic and aromatic hydrocarbons,esters, ethers, ketones and alcohols including such things as toluene,xylene, butyl acetate, acetone, methyl isobutyl ketone, butyl alcohol,etc. When using volatile organic solvents, although it is not required,it is preferred to include from about 2% to about 50% by weight of acellulose ester and/or wax (e.g., polyethylene) which facilitates quickrelease of the volatile organic solvent resulting in improved flow orleveling out of the coating. The cellulose esters used must becompatible with the particular resin systems selected and include suchthings as cellulose nitrate, cellulose propionate, cellulose butyrate,cellulose acetate butyrate, cellulose acetate propionate and mixturesthereof. The cellulose esters when used are preferably used in about 5%to about 20% by weight based on film forming solids.

The acrylic resins in the base coat may be either thermoplastic (acryliclacquer systems) or thermosetting. Acrylic lacquers such as aredescribed in U.S. Pat. No. 2,860,110 are one type of film formingcomposition useful according to this invention in the base coat. Theacrylic lacquer compositions typically include homopolymers of methylmethacrylate and copolymers of methyl methacrylate which contain amongothers, acrylic acid, methacrylic acid, alkyl esters of acrylic acid,alkyl esters of methacrylic acid, vinyl acetate, acrylonitrile, styreneand the like.

When the relative viscosity of the acrylic lacquer polymer is less thanabout 1.05, the resulting films have poor solvent resistance, durabilityand mechanical properties. On the other hand, when the relativeviscosity is increased above the 1.40 level, paints made from theseresins are difficult to spray and have high coalescing temperatures.

Another type of film forming material useful in forming the base coat ofthis invention is a combination of a crosslinking agent and acarboxy-hydroxy acrylic copolymer. Monomers that can be copolymerized inthe carboxy-hydroxy acrylic copolymer include esters of acrylic andmethacrylic acid with alkanols containing 1 to 12 carbon atoms, such asethyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate,2-ethylhexyl acrylate, lauryl methacrylate, benzyl acrylate, cyclohexylmethacrylate, and the like. Additional monomers are acrylonitrile,methacrylonitrile, styrene, vinyl toluene, alpha-methyl styrene, vinylacetate, and so forth. These monomers contain one polymerizableethylenically unsaturated group and are devoid of hydroxyl andcarboxylic groups.

The crosslinking agents used in combination with the hydroxy-carboxycopolymers are those compositions which are reactive with hydroxy and/orcarboxylic acid groups. Examples of such crosslinking agents arepolyisocyanates (typically di- and/or tri-isocyanates) polyepoxides andaminoplast resins. Particularly preferred crosslinking agents are theaminoplast resins.

The polyisocyanates when reacted with hydroxyl bearing polyester orpolyether or acrylic polymers will yield urethane films useful in theprocess of this invention in both the base coat and topcoat. Theisocyanate (--NCO) --hydroxyl (--OH) reaction takes place readily atroom temperature, so that ambient and low temperature cure is possible.

Among other base coats which are typically used in the processes of thepresent invention are those commonly known as alkyd resins which aredefined to include fatty acid or oil containing esterification products.The methods for preparing these resins are well known in the art.

The preferred alkyd resins useful in this invention are those containingfrom about 5 to about 65 weight percent of a fatty acid or oil andhaving an hydroxyl equivalent to carboxy equivalent ratio of from about1.05 to 1.75. Alkyd resins having less than about 5% fatty compound areclassified as the "oil-less" alkyd resins or polyester resins describedhereinafter. On the otherhand, alkyd resins containing greater than 65%of a fatty compound exhibit poor baking properties, poor chemicalresistance and unsatisfactory adhesion to either the base coat or thesubstrate. When the hydroxyl to carboxyl equivalent ratio is less thanabout 1.05 gelation can result during polymer preparation while resinsprepared having a ratio in excess of 1.75 have low molecular weights andtherefore poor chemical resistance.

These alkyd resins can also be used as the topcoat of this invention.When this is the case it is preferred that the oil or fatty acid portionof the alkyd resin contain a light colored baking oil or fatty acid suchas coconut or dehydrated castor oils or fatty acids. Furthermore, whenthese resins are used as topcoats they can be reacted with variousacrylic or ethylenically unsaturated monomers as described above toproduce vinyl modified alkyd resins.

Curing of these alkyd resins can be accomplished by blending with any ofthe previously described crosslinking agents in the same weight ratiosas are used with carboxy-hydroxy copolymers.

Included among the various fatty acids and oils useful in preparingthese alkyd resins are the fatty acids derived from the following oils;castor, dehydrated castor, coconut, corn, cottonseed, linseed, oticica,perilla, poppyseed, safflower, soybean, tung oil, etc., and the variousrosins containing tall oil fatty acids. Useful polyols include thevarious glycols, such as ethylene glycol, propylene glycol, neopentylglycol, butylene glycol, 1, 4 butanediol, hexylene glycol, 1,6hexanediol, the polyglycols such as diethylene glycol or triethyleneglycol, etc.; the triols such as glycerine, trimethylol ethane,trimethylol propane, etc., and other higher functional alcohols such aspentaerythritol, sorbitol, mannitol, and the like. Acids useful inpreparing the alkyd resins of this invention include mono-functionalacids such as rosin acids, benzoic acid, para tertiary butyl benzoicacid and the like; the polyfunctional acids such as adipic acid, azelaicacid, sebacic acid, phthalic acid or anhydride, isophthalic acid,terephthalic acid, dimerized and polymerized fatty acids, trimelliticacid, and the like.

Yet another useful base coat is prepared using non-aqueous dispersionssuch as are described in U.S. Pat. Nos. 3,050,412; 3,198,759; 3,232,903;3,255,135. Typically these dispersions are prepared by polymerizing amonomer such as methyl methacrylate in the presence of a solvent inwhich polymers derived from the above monomer are insoluble and aprecursor which is soluble in the solvent. Nonaqueous dispersions canhave a relative solution viscosity as previously defined of about 1.05to 3.0. Dispersions having a relative solution viscosity in excess ofabout 3.0 are difficult to spray and have high coalescence temperatureswhile dispersions with a relative solution viscosity less than about1.05 have poor resistance, durability and mechanical properties. Themonomers useful in preparing the above dispersed copolymers orhomopolymers are those listed previously as useful in forming thecarboxy-hydroxy acrylic copolymers.

In another instance the base coat film can be produced from resins knownas polyesters or "oil-less" alkyd resins. These resins are prepared bycondensing non-fatty containing polyols and polyacids. Included amongthe useful polyacids are isophthalic acid, phthalic acid or anhydride,terephthalic acid, maleic acid or anhydride, fumaric acid, oxalic acid,sebacic acid, azelaic acid, adipic acid, etc. Mono basic acids such asbenzoic, para tertiary butyl benzoic and the like can also be utilized.Among the polyalcohols are the diols or glycols such as propyleneglycol, ethylene glycol, butylene glycol, 1, 4 butanediol, neopentylglycol, hexalene glycol, 1,6-hexanediol, and the like; the triols suchas trimethylol ethane, trimethylol propane and glycerine and variousother higher functional alcohols such as pentaerythritol.

Any of the above-recited polymers may be used as the topcoat, as long asit provides a transparent film. The term "transparent film" is definedas a film through which the base coat can be seen. It is preferred thatthe transparent film be substantially colorless so that the fullpolychromatic and aesthetic effect of the base coat is not substantiallydecreased. However, in some instances, desirable and unique stylingeffects can be obtained by the addition of contrasting or complementarycolors to the topcoat. Another outstanding feature of the topcoat is thesignificant improvement in the durability which is provided to theoverall coating composition.

The unique aesthetics of this system require the iron oxide encapsulatedmica in the topcoat to be randomly located throughout the depth, width,and length of the clear film. In conjunction with the randomdistribution, the mica must also be oriented off both the vertical andhorizontal axes. This distribution and orientation assures thevisibility of the mica regardless of the viewing angle (90°, acute orobtuse). While this is in some degree a function of the particularcoating method utilized, it is also a function of the size andconstitution of the particle as described above. A Ransburg turbobellelectrostatic sprayer is particularly suitable for applications of thetransparent topcoat film containing the iron oxide encapsulated mica ofthe present invention.

The Figure which is a photomicrograph of a cross section of a coatedsubstrate according to the present invention demonstrates some of theunique aspects of the coating system according to the present invention.The thin white line below the terms "Hand Application" and"Cross-Section" represents the top (outermost portion) of the iron oxideencapsulated mica containing transparent topcoat. The base coat is asmarked and the substrate lies just below the base coat. The long whiteline segments in the topcoat ("Clearcoat") portion are the iron oxideencapsulated mica particles. The random orientation, uniform populationdistribution and lack of protrusion of the particles through the top ofthe transparent topcoat are demonstrated by the Figure and are all keyfactors which contribute to the improved properties of the transparenttopcoat containing the iron oxide encapsulated mica particles.

Utilizing the compositions of the present invention offers a means ofcombining the desirable properties of a combination of resin systems.For example, in automotive finishes the pigment control properties ofacrylic lacquers can be combined with the chemical resistance propertiesof thermosetting acrylic resins by applying a thermosetting acrylicclear coat containing iron oxide encapsulated mica particles over apigmented thermoplastic acrylic lacquer base coat (although acryliclacquers may be used for both layers). Likewise, in appliance finishesthe chemical resistance of polyester resins can be combined with thelower cost of thermosetting acrylic resins by applying a polyester cleartopcoat containing iron oxide encapsulated mica particles over apigmented thermosetting acrylic base coat. Although any of theabove-mentioned thermoplastic materials may be used to form thetransparent topcoat, better durability is achieved if the topcoat is oneof the above-cited thermosetting materials, i.e., the materialcontaining the crosslinking agents.

In all instances where the above methods and compositions are usedextremely high gloss films result. In fact, where with normal two coatsystems a 60° gloss in excess of 90-95 is difficult to obtain, using theprocess of this invention gloss readings in excess of 100 are readilyobtained.

The iron oxide encapsulated mica pigments according to the presentinvention are commercially available from the Mearl Corporation and EMChemicals, and range in color from golden bronze at the thinnest ironoxide encapsulation through copper, to red at the thickest iron oxideencapsulation. The iron oxide coatings on these pigments beingtransparent act as natural ultra-violet absorbers. For additionalexterior durability (e.g., exposure to the sun) minor amounts of otheradditives such as chromium hydroxide and titanium dioxide may beincluded in the iron oxide encapsulation layer. It should also be notedthat other high temperature stable metal oxides (such as copper,calcium, cadmium, cobalt, barium, strontium, manganese, magnesium andlithium) can be substituted in whole or in part for the encapsulatingiron oxide. The iron oxide encapsulation layer is generally in themolecular range of thicknesses representing about 10% to about 85% byweight of the total weight of the encapsulated mica particle, preferablyabout 20% to about 60%, and typically about 29% to about 48% by weight.If additives such as titanium dioxide or chromium hydroxide are used aspart of the encapsulation layer they are generally present in an amountof about 1% to about 35% by weight, and typically about 2% to about 5%for the titanium dioxide, and about 0.1% to about 3.5% by weight for thechromium hydroxide, based on total weight of the encapsulated particle.

The uniformity of shape (platelet) and smoothness of the iron oxideencapsulated mica pigment according to the present invention (e.g., ascompared to the highly fragile, three dimensional and complicatedconfiguration of aluminum flake, a standard in the automotive paintindustry) eliminates the problem of color drift due to the shear forces(yielding fragmentation problems) in the handling (overhead pumpingfacilities) and application problems of ghosting, mottling, silkinessand repair color matching.

The iron oxide encapsulated mica pigments are optically pearlescentbecause their transparency permits light to pass through the particleresulting in a multiplicity of refractions and reflections. In additionto their pearlescence these pigments have inherent hiding capabilities,are additive colors and retain a metallic appearance (face to flop colortravel). These features provide the capability of producing colors withdepth, clarity and chromaticity not previously attainable withconventional metals (i.e., aluminum) and previous pearlescent pigments(natural or synthetic) which produced colors lacking depth andchromaticity or color travel due to the aesthetics of the metalcomponent (aluminum) or pearl. These colorless and opaque pigmentsreduced the value (color intensity) of the "true" colored pigments bethey organic or inorganic resulting in gray-cloudy-low chroma colors.The addition of the iron oxide encapsulated mica pigments provideshiding and depth to travel with the aesthetically pearlescentappearance.

The iron oxide encapsulated mica pigments are carefully screened andcontrolled particles, all within about 5 microns to about 60 microns(preferably about 5 microns to about 45 microns, and typically about 5microns to about 35 microns) in their largest dimension, and about 0.25micron to about 1.0 micron in thickness. The closely controlled particlesize provides the transparent, translucent, reflective and refractivefeatures establishing improved aesthetic and physical properties ofthese coatings through careful selection and blending of these pigments.In admixture with conventional colored pigments (organic or inorganic)or dyes (natural or synthetic) unique pearlescent colors can beproduced. Blending complementary colors (e.g., red iron oxideencapsulated mica with red pigments or dyes) will produce deep chromaticcolors while blending contrasting colors (e.g., bronze iron oxideencapsulated mica with red or blue pigments or dyes) will produce highlychromatic colors with unique undertones. Regardless of the selection,the final (clear coated) enamel will have improved color durability,greater moisture resistance and greater acid resistance than coatingsprepared with conventional metals or synthetic pearls.

The amount of pigment in the base coat generally comprises about 1% toabout 20% by weight, preferably about 7.5% to about 15% and typicallyabout 10% by weight. About 5% to about 90% of this pigment can be ironoxide encapsulated mica according to the present invention, preferablyabout 25% to about 70% and typically about 60% by weight.

Both the base coat and the top coat can be applied by any conventionalmethod in this art such as brushing, spraying, dipping, flow coating,etc. Typically spray application is used, especially for automotivefinishing. Various types of spraying can be utilized such as compressedair spraying, electrostatic spraying, hot spraying techniques, airlessspraying techniques etc. These can also be done by hand or by machine.

As stated above prior to application of the coating materials of thepresent invention a conventional corrosion resistant primer has alreadybeen applied. To this primed substrate is applied the base coat. Thebase coat is typically applied from about 0.4 mil to about 2.0 mil andpreferably about 0.5 mil to about 0.8 mil. This thickness can be appliedin a single coating pass or a plurality of passes with very brief drying("flash") between applications of coats.

Once the base coat has been applied the transparent overcoat containingthe iron oxide encapsulated mica particles is applied after allowing thebase coat to flash at ambient temperature for about 30 seconds to about10 minutes, preferably about 1 to about 3 minutes. While the base coatcan be dried for longer periods of time, even at higher temperatures, amuch improved product is produced by application of the transparenttopcoat containing the iron oxide encapsulated mica particles after onlya brief flash. Some drying out of the base coat is necessary to preventtotal mixing of the base coat and topcoat. However, a minimal degree ofbase coat-topcoat interaction is desirable for improved bonding of thecoatings. The topcoat is applied thicker than the base coat (preferablyabout 1.8 to 2.3 mils) and can also be applied in a single or multiplepass. It should also be noted that the iron oxide encapsulated micapigments are applicable at low levels in the clear coat and in basecoats with tinted clear topcoats. Both applications produce uniqueaesthetics while retaining the pearlescent appearance.

Pigment control is retained in the base coat while it is beingovercoated. This is evidenced by lack of "strike-in" or migration of thetwo films (the base coat and topcoat) into each other. When "strike-in"occurs, pigments move from the base coat into the topcoat, the filmcompositions become intermixed at the interface and the baked coatingcomposition has a dusty appearance rather than a clear "depth"appearance. By this invention substantially no "strike-in" occurs, andthe coatings have outstanding clarity and depth. However, sufficientwetting takes place at the interface so that no problems of delaminationand solvent release from either coating are obtained.

Once the topcoat is applied the system is again flashed for 30 secondsto 10 minutes and the total coatings are then baked at temperaturessufficient to drive off all of the solvent in the case of thermoplasticlayers and at temperatures sufficient to cure and cross-link in the caseof thermosetting layers. These temperatures can range anywhere fromambient temperature to about 400° F. Typically in the case ofthermosetting material temperatures of about 225° F. to about 280° F.(e.g., 250° F.) are used, (e.g., for about 30 minutes).

The following examples are illustrative of the principles and practiceof this invention although not limited thereto. Parts and percentageswhere used are parts and percentages by weight.

Three iron oxide encapsulated mica pigments are used in the followingexamples. The Golden Bronze Richelyn™ (Inmont Corporation) pigmentcomprises 62%-68% mica, 29%-35% iron oxide, (Fe₂ O₃), 3%-5% titaniumdioxide (TiO₂) and 0.3%-0.9% chromium hydroxide (Cr(OH)₃). The RedRichelyn pigment comprises 49%-55% mica, 42%-48% iron oxide, 2%-4%titanium dioxide, and 0.3% to 0.9% chromium hydroxide. The CopperRichelyn pigment comprises 51%-57% mica, 40%-46% iron oxide, 3%-5%titanium dioxide and 0.3%-0.9% chromium hydroxide. All percents are byweight based on the total weight of the encapsulated pigment. The GoldenBronze Richelyn pigment contains a relatively thin layer of iron oxideencapsulation, the Red Richelyn pigment contains a relatively thicklayer of iron oxide encapsulation, and the Copper Richelyn pigmentcontains a layer of iron oxide encapsulation which is somewhere inbetween.

EXAMPLE 1

A silver gray "metallic" base coat polymer composition was prepared byblending 144 parts of the copolymer formed by reacting 47 parts of butylmethacrylate, 37 parts of styrene, 15.75 parts of hydroxypropylmethacrylate and 0.25 part of methacrylic acid with 176 parts of xyleneand butanol (in a weight ratio of 85/15). A pigment base was prepared byblending 99.77 parts of Rutile Titanium Dioxide with 0.22 part carbonblack and 0.01 part Indanthrone Blue. This pigment base was blended withthe base coat polymer composition in an amount representing 7.5% byweight of the composition to form the base coat paint composition.

Bonderized steel panels primed with a cured corrosion resistant primerwere sprayed with the base coat paint composition to a film thickness of0.6 mil on a dry film basis. After a flash of approximately 2 minutes atroom temperature an additional 0.6 mil film of the base coat paintcomposition again as measured on a dry film basis was applied byspraying. After a 2 minute flash at room temperature, a transparent topcoating containing Golden Bronze Richelyn pigment in a 0.001 pigment tobinder ratio was applied by spraying to a film thickness on a dry basisof 2 mils. The transparent topcoating composition was prepared byblending 144 parts of the copolymer solution described above at 45percent nonvolatiles with 58 parts of 60 percent nonvolatile solution ofbutylated methylol melamine. The thus coated substrate was baked at 250°F. for 30 minutes. The coating has a pleasing aesthetic appearance,exhibiting superior polychromatic effects and silver "metallic"appearance.

EXAMPLE 2

Using the procedure of Example 1 a base coat pigment compositionrepresenting 7.478% pigment in the base coat, comprising 95.00 partsRutile Titanium Dioxide, 4.50 parts phthalocyanine blue, and 0.50 partcarbon black was overcoated with the same transparent topcoat ofExample 1. A light-medium blue "metallic" coated substrate resulted. Allcoatings were applied with a Ransburg turbobell electrostatic sprayer (3inch diameter, 5/8 inch depth) at a traverse speed of 14 ft/min., 12-14inch standoff, 30,000 rpm, at a voltage of about 110 Kv.

The compositions and processes according to the present inventionprovide many improvements over the paint compositions and processes ofthe prior art. Pearlescent color effects at least equivalent to the useof metallic particles are produced without the need for metal particlesand the application and stability problems associated with them. Novelcolor effects can be produced. Better hiding of surface defects can beproduced. Color, hiding, fineness of particle size and reflectance notavailable with other pearlescent pigments are produced while maintainingthe appealing and desirable soft, lustrous appearance characteristic ofpearlescent. Blending with organic and/or inorganic pigments (includingmetal particles) is possible with enhancement of aesthetic effectsproduced. Weather durable color effects are produced.

The applied compositions are not moisture sensitive, use relativelysmall particle size, are less sensitive to criticality of applications,maintain color trueness at all angles (face to flop color travel), canwithstand the elements (i.e., sun exposure), do not operate withsubtractive color effects when mixed with other pigments, allow low bakerepair color matching, and resist settling and chemical (e.g., acidrain) attack.

It should be noted that while the compositions of the present inventionare particularly adapted for original equipment manufacture coatings forautomobiles, one of their advantages is the low bake matching use asrefinish compositions as well. Whereas in original equipment manufacturethe disclosed cellulose esters and/or wax are typically used, such arenot universally required for example in refinish compositons. Also,where the thermosetting polymer embodiments are preferred in theoriginal equipment manufacture, in refinish either low temperature curethermosetting materials (e.g., 150° to 180° F.) or ambient temperaturecure thermosetting or thermoplastic materials are preferred.

A big advantage of the transparent topcoat of the present invention isthe extremely low pigment to binder ratio of iron oxide encapsulatedmica necessary to produce the improved, unique, aesthetic effects andprotective qualities of the present invention. Typical pigment to binderratios range from about 0.0001 to 0.32 (by weight) and preferably about0.001. The iron oxide encapsulated mica particles in the topcoat alsoprovide a multiplicity of prismatic variation both due to the presenceof the particles in the topcoat and due to the light reflective andrefractive properties of the particles themselves, i.e., the individuallayers on the mica particles. This also provides exceptional colorcontrol not obtainable with traditional systems or metal flakes.

Another advantage of the system according to the present invention isthe durability of the coating. The iron oxide encapsulated micaparticles are natural ultraviolet light absorbers. This providesprotection not only to the polymer base but the organic and inorganicpigments as well. For automobile use this provides extended weatheringdurability.

The topcoat coating material having a low pigment to binder ratio ofiron oxide encapsulated mica pigments does not alter the rheology of theclear coating. This allows application over both poor and excellentrheological base coats with excellent aesthetic qualities resulting.This offers enamel systems with improved rheology over traditionalenamels. Furthermore, the iron oxide encapsulated mica pigments in theclear coat provide a reinforcing mechanism for the clear coat to thebase coat resulting in a better anchored coating system.

In the method area the highly critical parameters necessary for variouscoating procedures such as electrostatic spraying required by the use ofmetal flakes is no longer a problem with the material of the presentinvention. In addition, the method of the present invention producesgreater pump stability in the lengthy paint lines required in mostautomotive applications. With metal flakes in the paint not only is pumpstability a problem but the shearing effect on the metal flake altersthe original color.

The paints according to the present invention all have improved heatstability over conventionally used paint and improved chemicalresistance over metal particle-containing paints. Another advantage isthe volume to weight ratio of solids in the paints with the eliminationof metal particles and as mentioned above the low pigment to binderratios useable with the present invention.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

I claim:
 1. A transparent coating composition particularly adapted foruse in automotive coatings consisting essentially of thermoplastic orthermosetting resin containing iron oxide encapsulated mica particles ina particle to weight ratio of about 0.0001 to about 0.32, the iron oxideencapsulation additionally containing about 1% to about 35% titaniumdioxide and about 0.1% to about 3.5% chromium hydroxide, based on totalweight of the particle, the mica particles being about 5 microns toabout 60 microns nominal longitudinal dimension and having a thicknessof about 0.25 micron to about 1 micron, the iron oxide encapsulationrepresenting about 10% to about 85% by weight of the total weight of theparticle, the composition when used as a transparent topcoat portion ofa multicoat coating system producing metallic color effects andstability to the elements.